Ask The Pilot

[Boris spatsky]

Thx JB:

If a flight departs late, sometimes we hear flight crew saying they will try to make up time.

Can this actually happen? - say by going faster, taking a different route?

There are various ways to make up time but they all have their limitations: go faster, find a level with less headwind/more tailwind, reduce your track miles (i.e cut the corners).

We are allowed to go faster up to a set limit (or Cost Index) - the aircraft can go faster, but the company won't allow it for cost reasons as it burns more fuel. It is also only really beneficial on longer sectors as the speed increase on short sectors might only save you a few minutes at best. On Long haul legs, going faster has better benefit than on short haul (but fuel then becomes the issue).

Cutting corners is normally at the whim of ATC and on short sectors doesn't save you much time anyway. Flying a shorter approach such as a visual approach may save you a few minutes as can picking the best taxiway to exit the runway at, but this is is all 1-2 minute savings, not 30+.

Changing levels can help also but it is a fairly complex exercise as you have to pick the best level that accounts for not only the wind at that level, but the TAS as well and a different fuel burn. Going lower might reduce a headwind, but the increased fuel burn might not make it worthwhile. Most aircraft FMS can help to work out the optimum level.

On short haul, the best way to make up time is on the ground (depart ASAP!)

 

[Quickstatus]

Thanks Boris....


further:

The departure and arrival times seen on an online booking....What do these times actually refer to?... And do those times also include a contingency for delays?

 

[Boris spatsky]

The flight times shown are off blocks (pushback), and on blocks (stopping at the gate), as far as i am aware.

Flight schedules are average times over the sector and vary month to month (due prevailing winds in different months) and updated due to issues like runway works (i.e planned taxiway works at say, Sydney, might mean an extra 10 mins is scheduled).

To be honest, the scheduling is a bit of an unknown to us as to how they work it out - you get to know some sectors where you will normally be early etc, and others where there is very little 'fat' to allow for unexpected delays.

 

[Quickstatus]

Thx Boris

Im looking at some transpacific flights on Flightaware. At some point USA bound and oZ bound flights will pass one another . maybe around 2200 AEST.

Do pilots chat to other pilots on other flights? If so is it general chit chat or maybe an exchange of technical jnfo such as weather etc etc

 

[jb747]

Thx JB:

If a flight departs late, sometimes we hear flight crew saying they will try to make up time.

Can this actually happen? - say by going faster, taking a different route?

If there is a 'better' route, then they'll already be on it.

On short sectors there is very little that can be done. Cruising lower and faster might get a minute or two. A delayed descent, with full speed brakes all the way, can save about 3 minutes, but it's uncomfortable, and rarely worth it.

Longer sectors offer more options. You can normally save about a minute per hour, as long as you have the fuel. On a 15 hour flight, that 15-20 minutes saved will result in a fuel burn increase measured in tonnes. Sometimes long flights to curfew constrained airports are planned at lower than usual cost indexes, and you can retrieve a few minutes from them. The upshot though, is that it's very easy to lose time, but virtually impossible to make up more than small periods.

 

[jb747]

Im looking at some transpacific flights on Flightaware. At some point USA bound and oZ bound flights will pass one another . maybe around 2200 AEST.

Do pilots chat to other pilots on other flights? If so is it general chit chat or maybe an exchange of technical jnfo such as weather etc etc

On most occasions, flight in opposite directions across the Pacific don't pass anywhere near each other. Routes can vary by a couple of thousand miles at the mid point.

Some nationalities are more inclined to 'chatting' than others. Given that everybody flies with the same frequencies selected, chatting is generally considered rude and unprofessional.

 

[Himeno]

Im looking at some transpacific flights on Flightaware. At some point USA bound and oZ bound flights will pass one another . maybe around 2200 AEST.

These are the QF AU-US flights from flight radar around 0830UTC yesterday.

 

[mikenz]

What makes an aircraft take off? Does the pilot need to do something to lift the nose? And what actually happens at that point?

 

[jb747]

What makes an aircraft take off? Does the pilot need to do something to lift the nose? And what actually happens at that point?

You pull back on the control column/joystick. That causes the elevator (on the horizontal tail) to tilt upwards. That generates a downward force in the tail, which pivots the aircraft around the main landing gear.

 

[Awesom Andy]

You pull back on the control column/joystick.

Speaking of which, would you pull it as much/little as necessary, or would you just yank it all the way and let the electronics handle the rest? (A380 and other airbus types only, of course).

 

[Quickstatus]

Thx JB:

If an aircraft is travelling at 500kts, how does Jetfuel get ignited in a modern turbofan engine.

My understanding is that Jetfuel is very difficult to ignite unless atomised, but if the airflow is at 500 kts how can ignition occur

Maybe pressures are increased and airspeed reduced within the Jet engine causing ignition is a very hot environment?

 

[jb747]

Thx JB:

If an aircraft is travelling at 500kts, how does Jetfuel get ignited in a modern turbofan engine.

My understanding is that Jetfuel is very difficult to ignite unless atomised, but if the airflow is at 500 kts how can ignition occur

Maybe pressures are increased and airspeed reduced within the Jet engine causing ignition is a very hot environment?

In an engine, it is atomised. And it's also extremely hot.

Ignition, in the form of big spark plugs is provided at startup, but most of the time, it's simply a continuous flame with no ignition source other than the already burning fuel.

 

[mjt57]

In an engine, it is atomised. And it's also extremely hot.

Ignition, in the form of big spark plugs is provided at startup, but most of the time, it's simply a continuous flame with no ignition source other than the already burning fuel.

JB, ever watched the igniters operate outside of the engine? The ones on our gas turbines were quite large and aside from the huge arc the crack that they made was louder than say, a 30-30 going off next to you.

 

[jb747]

Speaking of which, would you pull it as much/little as necessary, or would you just yank it all the way and let the electronics handle the rest? (A380 and other airbus types only, of course).

You have to actually fly the rotation. The amount and rate of pull varies every time, and even during the 3-4 seconds that it takes.

'Yank' should never be a term associated with any control input.

The Airbus electronics will not handle a rotation. In fact they are quite limited at that point (and near the flare) as the aircraft is basically in direct law for pitch. Normal law comes into play a few seconds after liftoff.

The rotation has to be flown with some care. Do it too slowly and you'll use up more runway and end up faster than desired. Too fast, and you'll probably lift off early at a slower than desired speed, and at a higher pitch attitude. Tail strikes can easily come into play here.

 

[RooFlyer]

If there is a 'better' route, then they'll already be on it.

On short sectors there is very little that can be done. Cruising lower and faster might get a minute or two. A delayed descent, with full speed brakes all the way, can save about 3 minutes, but it's uncomfortable, and rarely worth it.

Longer sectors offer more options. You can normally save about a minute per hour, as long as you have the fuel. On a 15 hour flight, that 15-20 minutes saved will result in a fuel burn increase measured in tonnes. Sometimes long flights to curfew constrained airports are planned at lower than usual cost indexes, and you can retrieve a few minutes from them. The upshot though, is that it's very easy to lose time, but virtually impossible to make up more than small periods.

Looking at the reverse scenario. A couple of times my long haul flight has delayed taking off because (we were told) there were tailwinds and we'd arrive at the destination too early.

Say you were already in flight TPAC and encountered roaring tailwinds and you needed to slow down. Would the best option be to keep the existing course and reduce thrust (therefore I'm assuming over-ground velocity, but maybe with a drag penalty), or try to change course and/or altitude to allow you to get closer to your planned velocity and rate of fuel burn?

 

[jb747]

Looking at the reverse scenario. A couple of times my long haul flight has delayed taking off because (we were told) there were tailwinds and we'd arrive at the destination too early.

Say you were already in flight TPAC and encountered roaring tailwinds and you needed to slow down. Would the best option be to keep the existing course and reduce thrust (therefore I'm assuming over-ground velocity, but maybe with a drag penalty), or try to change course and/or altitude to allow you to get closer to your planned velocity and rate of fuel burn?

I've never been a big fan of losing time at the gate. The problem is that it's far too easy to have ATC, or congestion, or a million other factors, add more lost time than you really wanted...and then you've gone from being early and wanting to get rid of time, to being late.

If you are already underway, and will still arrive too early, do you actually have a real problem? You could slow down, though there is a limit to that, and there's not too much more variation available on the slowing side of the operation than there is speeding up (i.e. you can slow about .03 mach...and you can normally speed up by a similar amount). If you need slower than you'll have to go lower...and whilst the timings might work, it's inefficient, and will ultimately cost you more fuel.

Generally when curfew constrained, I try to get to the airport holding fix about 10-15 minutes before the end of the curfew. The chances are quite good that that will have me first or second in the queue, and after one or two runs around the pattern we'll be crossing the fence within seconds of the curfew end. Arriving later ends up counter productive, as you'll hold for longer, and end up losing much more time. Arriving on QF1 to London that's a good tactic.

In the more congested parts of the world, the ability to adjust your speed is quite limited. If you slow down, the bloke behind you is likely to have issues...so ATC often assign minimum or maximum speeds.

 

[juddles]

.....'Yank' should never be a term associated with any control input.....

With the posible exception of ejection seats?

 

[RooFlyer]

I've never been a big fan of losing time at the gate. The problem is that it's far too easy to have ATC, or congestion, or a million other factors, add more lost time than you really wanted...and then you've gone from being early and wanting to get rid of time, to being late.

If you are already underway, and will still arrive too early, do you actually have a real problem? You could slow down, though there is a limit to that, and there's not too much more variation available on the slowing side of the operation than there is speeding up (i.e. you can slow about .03 mach...and you can normally speed up by a similar amount). If you need slower than you'll have to go lower...and whilst the timings might work, it's inefficient, and will ultimately cost you more fuel.

Generally when curfew constrained, I try to get to the airport holding fix about 10-15 minutes before the end of the curfew. The chances are quite good that that will have me first or second in the queue, and after one or two runs around the pattern we'll be crossing the fence within seconds of the curfew end. Arriving later ends up counter productive, as you'll hold for longer, and end up losing much more time. Arriving on QF1 to London that's a good tactic.

In the more congested parts of the world, the ability to adjust your speed is quite limited. If you slow down, the bloke behind you is likely to have issues...so ATC often assign minimum or maximum speeds.

Thanks again . I suspect we'll have different views on this, but I'm not hugely enthusiastic about arriving early - say 1/2hr or more after long haul. Yes, we are on the ground, so ATC can't stuff us around, but invariably I find that after the cheery "We're early" announcement comes the downer - "the gate is occupied, so we'll just have to park here for a while."

I know it makes b-all difference to when we get away from the airport, but I'd rather have a longer in-air journey and hence have the freedoms that that entails, over landing early and being strapped in for an extended period. Of course, in the grand scheme of things, not a big deal.

 

[Flashback]

Just on the toilets question again ... I flew RAK-LGW on a BA 737-436 and it had the swirling blue liquid to flush down

 

[Trakman]

I was waiting to take off from MEL the other day in a queue because the high winds had closed the other runway.

Watching the spacing of aircraft landing and taking off, it seemed that they were allowing much longer times than I see with overseas airports. A couple of times as a flight was coming in to land I know that in the US they would have let one of the departing aircraft take off ahead of it.

Is there much of a difference in the amount of spacing that ATC allow between planes, and does it vary from country to country or airport to airport?